This invention relates to an improved spool for winding a photographic roll film, and particularly to a spool for winding a roll film accommodated in a film unit with a lens (film and lens units).
Recently, film and lens units or so-called disposable cameras are appearing on the market. Namely, the film and lens unit itself is designed to constitute a simple camera by attaching a lens to a cartridge for accommodating a roll film to enable photographing by feeding the film frame by frame.
The film and lens unit usually comprises a cartridge with a lens accommodating a roll film of type 135 in a patrone and a slotted spool disposed outside of the patrone; wherein the tongue of the film extending from the patrone is designed to be inserted into the slit formed on the spool, and the film in the patrone is wound up fully onto the spool with the tail end of the film being firmly retained in the patrone.
Further, when the film is completely used through photographing, the film once wound up on the spool is rewound into the patrone since the film has been fed back frame by frame as the photographing proceeded. In this state, the film unit is sent to a photo-finishing laboratory. At the laboratory, the film and lens unit is disassembled to take out the patrone and then the roll film is subjected to an ordinary developing process for type 135 film.
As shown in FIG. 9 (front view) and FIG. 10 which shows a cross-sectional view taken along line A--A of FIG. 9, the spool (1) has a roll shaft (6) with a slit (7) formed thereon. The slit (7) has holding ribs (9) and (8) respectively at inner walls (7a) and (7b) which are opposed to each other.
At both ends of the roll shaft (6), flanges (5) are respectively provided. Further provided coaxially to the roll shaft (6) are bosses (2) and (3) at both outer sides of the flanges (5), and a drive transmission joint (4) at the end of one boss (3).
When the film is allowed to be wound up on the spool (1) after the tongue of the roll film contained in the patrone is inserted into the slit (7) formed on the roll shaft (6) of said spool (1), it is essential to prevent the film from slippage out of the slit (7) at the initial stage of winding. On the other hand, when the film is completely used, it is essential that said tongue is easily released from the slit (7) of the spool (1) and rewound completely or nearly completely into the patrone.
In particular, if the tongue slips out of the slit (7) at the initial stage of winding, the unit is defective and is not usable as a camera. On the other hand, if the tongue is not released from the slit (7) even after completion of photographing with the film, some portion of the used film adjacent to the tongue remains outside of the patrone, so that said portion of the film is exposed to light and suffers light fog when the used film is taken out from the cartridge by disassembling the film and lens unit. Accordingly, the results of the user's photography are spoiled at the exposed portion.
Consequently, it is essential required for the spool (1) to be designed so that the slit (7) firmly holds the tongue of the roll of film at the initial stage of winding the film, and that slit 7 easily releases the tongue at the end of photographing with the film. Conventional spools cannot perform these tasks reliably and repeatedly.
Moreover, when the tongue is inserted into the slit (7) in the conventional spools, the tongue sometimes extends through the slit to protrude from the opposite opening of the slit (7), as shown in FIG. 11. If the film is wound up in such state, the protruding portion of the tongue causes the wound film roll to be distorted. Therefore, so-called pressure fog is liable to be caused at the distorted portions.